Butenes and butanes are products in high industrial demand and are usually obtained by working up cuts comprising C4-hydrocarbons from steam or naphtha crackers. In the available raw material sources, the different isomers of the butenes and butanes and also butadiene are typically present in varying proportions. Butadiene may either be converted to n-butenes by hydrogenation or removed from these mixtures by extractive distillation. For further workup of the butenes and butanes, it is frequently necessary to separate them from each other. As a consequence of the very close proximity of their boiling points, it is generally not possible to achieve the purities required by simple distillation. As such, it is necessary to resort to other separating processes, including extractive distillation using polar solvents, such as disclosed in US20060096849.
Unfortunately, use of polar extractants, such as a mixture of N-methylpyrrolidone (NMP) and water, may result in undesirably high concentrations of water in the butene product, if not handled properly. Additionally, use of such mixtures adds the potential for formation of separate hydrocarbon and aqueous phases on trays or packing in a tower, which may reduce the separation efficiency of the tower.